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�Corresponding autMississippi State, M

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Technical note

Separation of fiber from distillers dried grains (DDG) usingsieving and elutriation

Radhakrishnan Srinivasana,�, Robert A. Moreaub, Carl Parsonsa,John D. Lanea, Vijay Singha

aUniversity of Illinois at Urbana-Champaign, Urbana, IL, USAbUS Department of Agriculture, Wyndmoor, PA, USA

a r t i c l e i n f o

Article history:

Received 17 July 2007

Received in revised form

30 October 2007

Accepted 31 October 2007

Available online 20 February 2008

Keywords:

Elusieve

Air classification

Zea mays

nt matter & 2007 Elsevieioe.2007.10.013

hor. Current address: DepS 39762, USA. Tel.: +1 662adha@abe.msstate.edu (

a b s t r a c t

In the dry-grind corn-to-ethanol process, distillers wet grains (DWG) and syrup are blended

and dried to produce distillers dried grains with solubles (DDGS). Some dry-grind plants

produce distillers dried grains (DDG) as a coproduct instead of DDGS. In these plants, syrup

is not mixed with DWG and is sold as a liquid food ingredient or used for energy generation

by combustion. We showed recently that, the elusieve process, the combination of sieving

and elutriation (upward air flow), was effective in separating fiber from DDGS. The elusieve

process could be beneficial in separating fiber from DDG also. In this study, fiber separation

from DDG using the elusieve process was evaluated. Elutriation of sieve categories

increased neutral detergent fiber (NDF) in the lighter fractions and NDF separation factors

were more than 1.0. When DDG is separated via the elusieve process, 11.9% would be

obtained as elusieve fiber and 88.1% would be obtained as enhanced DDG. Original DDG had

NDF of 36.7% (db), while enhanced DDG would have NDF of 35.3% (db) and elusieve fiber

would have NDF of 57.3% (db). Thus, elusieve process produces value-added products from

both DDG and DDGS. A detailed economic analysis is needed to ascertain the merits of

implementing the elusieve process in a dry-grind plant producing DDG instead of DDGS.

& 2007 Elsevier Ltd. All rights reserved.

1. Introduction

In the dry-grind corn-to-ethanol process, cornstarch is

fermented to produce ethanol [1]. The solution of ethanol

and water is distilled to obtain ethanol. The underflow from

the distillation column (called whole stillage) is centrifuged to

obtain distillers wet grains (DWG) that contain 30–35% solids

[1]. A part of the centrifuge supernatant (called thin stillage) is

recycled to the slurry preparation tank and the remaining

thin stillage is concentrated to obtain syrup (also called

distillers solubles) that contains 25–40% solids [1]. DWG and

r Ltd. All rights reserved.

artment of Agricultural325 8536; fax: +1 662 325

R. Srinivasan).

syrup are blended and dried to produce distillers dried grains

with solubles (DDGS).

Some dry-grind plants produce distillers dried grains (DDG)

as a coproduct instead of DDGS. In these plants, syrup is not

mixed with DWG and is sold as a liquid food ingredient or

used for energy generation by combustion [2,3]. When syrup

is not mixed with DWG, the coproduct formed from DWG is

DDG, defined as the product obtained after removal of ethyl

alcohol by distillation from the yeast fermentation of a grain

or a grain mixture by separating the resultant coarse grain

fraction of the whole stillage and drying [4].

and Biological Engineering, Mississippi State University, Box 9632,3853.

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A Midwestern dry-grind ethanol plant has been burning

syrup in a fluidized bed combustion unit to produce heat and

power [3]. There has been growing interest in the utilization

of coproducts for energy generation in dry-grind ethanol

plants due to the availability of feedstocks within the plants

and the need for reducing utility cost [5]. Some plants are

considering gasification and combustion of DDG and DDGS

for generating energy.

We recently reported that the elusieve process, the combi-

nation of sieving and elutriation (upward air flow), was

effective in separating fiber from DDGS [6]. By sieving DDGS

into different sieve categories and then air classifying the

sieve categories, fiber separation was effective because of

elimination of small-sized nonfibers. The elusieve process

resulted in ‘‘enhanced’’ DDGS that had lower fiber content

than DDGS and the ‘‘elusieve’’ fiber separated was an

additional coproduct.

Similarly, fiber separation from DDG could also be bene-

ficial. Separation of fiber from DDG would result in DDG with

enhanced nutritional characteristics due to lower fiber

content, and separated fiber can be used along with syrup

for energy generation. The current study was designed to

evaluate the elusieve process for the first time using DDG

instead of DDGS. The objectives of this study were to

determine (1) fiber content of DDG fractions from sieving

and elutriation, and (2) effect of air velocity on fiber removal

from DDG.

2. Materials and methods

DDG material was obtained from a state-of-the-art dry-grind

plant in Midwest US and stored at 4 1C. No microbial damage

was found on visual observation. A total of 30 kg of the

commercial DDG material was divided into three batches of

10 kg each to carry out elusieve processing in three replicates;

a sample was collected from each batch. Each batch of DDG

was sieved into five sieve categories using screens 16M

(1130mm), 24T (869mm), 34T (582 mm), 48T (389mm) and pan,

using the procedure described in [6] (Fig. 1). The five sieve

categories were referred to as 16M (41130mm), 24T

(869–1130mm), 34T (582–869mm), 48T (389–582mm) and pan

(o389mm), based on their respective sieve labels. Six samples

were available from sieving: five samples from each sieve

category and one original DDG sample.

Each of the four largest sieve categories was elutriated

using the 155 mm elutriation apparatus, described in Srini-

vasan et al. [7]. The pan sieve category was not elutriated

because it was visually observed that fiber content was low.

Material carried by air to the top of the elutriation column

Batch 1 (10 kg) – Sieving -

16M

24T

34T

48T

Pan

Elutriatat five avelociti

Fig. 1 – Experimental scheme for the elusieve process for bat

processed similar to batch 1.

was the lighter fraction; material that settled at the bottom

was the heavier fraction. The apparatus consisted of an

elutriation column, an air blower for supplying air to the

elutriation column, a surge box mechanism for controlling

airflow, a vibratory feeder for feeding material into the

column and collection vessels for receiving the lighter and

heavier fractions. Each of the four largest sieve categories was

elutriated at five air velocities to obtain lighter fraction yields

ranging from 15% to 50% (Fig. 1). Ten elutriation samples

(lighter and heavier fractions from each air velocity) were

available from each sieve category; 40 elutriation samples

were available per batch of DDG. Thus, there were 46 samples

per batch of DDG and a total of 138 samples from the three

batches of DDG.

Samples were analyzed for neutral detergent fiber (NDF)

using the procedure outlined by Van Soest et al. [8]. Sample

moisture contents were determined using the two-stage

convection oven method [9, Method 44-18]. NDF separation

factor (aNDF), the ratio of the NDF/non-NDF of the lighter

fraction to the NDF/non-NDF of the heavier fraction, was used

to quantify fiber separation by elutriation [6]:

aNDF ¼½NDF=ð100�NDFÞ�lighter fraction

½NDF=ð100�NDFÞ�heavier fraction.

The NDF separation factor was indicative of the selectivity of

air in carrying fiber rather than nonfiber at each air velocity.

A large NDF separation factor indicated high selectivity.

ANOVA analysis and Tukey’s test (SAS Institute, Cary, NC)

were used to compare means of compositions and yields from

elusieve processing of three batches. Statistical significance

level was 5% (po0.05).

3. Results and discussion

3.1. Sieving

The amount of material (wt%) in the five sieve categories 16M,

24T, 34T, 48T and pan was 27.2%, 22.8%, 21.4%, 15.0% and

13.5%, respectively, and the NDF values (db) were 38.8%,

36.8%, 34.6%, 32.2% and 27.7%, respectively. The pan sieve

category contained lower NDF (27.7%; db) than the original

DDG sample (36.7%; db). The pan sieve category was not

subjected to elutriation as it had low fiber content. COV for

wt% and NDF were less than 711%.

3.2. Elutriation—fiber separation

Elutriation was effective in separating fiber from sieve

categories as indicated by higher NDF in the lighter fractions

ionires

Yields(L) of ~ 15, 20, 25, 30 & 50%

Yields(L) of ~ 15, 20, 25, 30 & 50%

Yields(L) of ~ 15, 20, 25, 30 & 50%

Yields(L) of ~ 15, 20, 25, 30 & 50%

ch 1 of distillers dried grains (DDG). Batches 2 and 3 were

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and lower NDF in the heavier fractions compared with

the initial material (Table 1). NDF separation factors were

more than 1.0. For the 16M sieve category, elutriation

at 2.08 m s�1 increased NDF from 38.8% to 54.7% in the

lighter fraction. A total of 95–113% of NDF was accounted by

the material balance. COVs of NDF were less than 711%.

Mean moisture content of the initial material was 14.9%.

Mean moisture content of lighter and heavier fractions

was 8.9%.

Within a sieve category, an increase in air velocity increased

the weight of the lighter fraction and, in some cases, the

weight of the lighter fraction remained constant with

increased air velocity (Table 1). Within sieve categories,

NDF of lighter fractions decreased or remained constant with

increased air velocity. NDF decreased in the lighter fractions

because higher air velocities tended to carry nonfiber

components. There was no clear trend for NDF separation

factors within sieve categories (Table 1 and Fig. 2). For the 24T

sieve category, as air velocity increased from 1.75 to

1.92 m s�1, the lighter fraction yield increased from 7.2%

to 13.6%; NDF of the lighter fraction decreased from 63.1%

to 59.0%; NDF separation factor decreased from 2.7 to 2.2.

COVs of NDF were less than 711%. COVs of the lighter

fraction yield were less than 720%, except for the 34T sieve

category at 1.60 m s�1 (724.1%).

Table 1 – Yield and NDF (%db) of fractions from elutriation of s

Sieve category Velocity (m s�1) Yield (%) (L) Y

16M (41130 mm) 0� NA

2.08 12.7d

2.37 22.6c

2.50 28.1c

2.69 36.6b

2.92 44.8a

24T (869–1130 mm) 0� NA

1.75 7.2d

1.92 13.6dc

2.16 21.1c

2.37 33.3b

2.63 51.1a

34T (582–869 mm) 0� NA

1.60 7.6c

1.75 14.6cb

1.92 19.2b

2.23 40.3a

2.50 50.3a

48T (389–582 mm) 0� NA

1.55 14.8d

1.65 21.9dc

1.84 31.2c

2.08 48.9b

2.30 76.5a

NDF—neutral detergent fiber; H—heavier fraction; L—lighter fraction; NA

of three batches. Values in the same column of a sieve category followe� Values at 0 m s�1 denote initial material.

3.3. Comparison of fiber separation for DDGS and DDG

Elutriation was effective in separating fiber from DDGS

as well as DDG. Trends for NDF of the lighter fraction

with increase in air velocity were similar for DDG and

DDGS [6,7]. The NDF value of the lighter fractions at

lowest air velocities were comparable for DDGS and DDG,

56–67% for DDGS and 55–63% for DDG. NDF separation

factors at lowest air velocities were lower for DDG com-

pared with DDGS, 2.2–4.0 for DDGS and 2.0–3.0 for DDG.

Within sieve categories, NDF separation factors were

lower for DDG compared with DDGS for similar air velocities

(Fig. 2).

3.4. Products obtained by fiber separation from DDG

Elusieve fiber would be obtained by mixing lighter fractions;

enhanced DDG would be obtained by mixing heavier fractions

and pan material. Yields and NDF values of elusieve fiber and

enhanced DDG were determined based on 15% lighter

fraction yield from each of the four largest sieve categories,

corresponding to air velocities of 2.08, 1.92, 1.75 and 1.55 m s�1

for 16M, 24T, 34T and 48T, respectively (Table 1). Of

the original DDG material, 11.9% would be obtained as

elusieve fiber and 88.1% would be obtained as enhanced

ieve categories of DDG

ield (%) (H) NDF

L H Separation factor

NA 38.8b 38.8a NA

87.3 54.7a 38.1a 2.0

77.4 50.2a 37.6a 1.7

71.9 50.1a 37.9a 1.6

63.4 49.0a 35.9a 1.7

55.2 47.5a 37.0a 1.5

NA 36.8c 36.8a NA

92.8 63.1a 38.9a 2.7

86.4 59.0ba 39.2a 2.2

78.9 56.0ba 37.6a 2.1

66.7 52.6b 35.9a 2.0

48.9 49.8b 33.7a 1.9

NA 34.6d 34.6ba NA

92.4 62.4a 35.8a 3.0

85.4 58.5ba 35.1ba 2.6

80.8 56.9cba 34.2ba 2.5

59.7 49.8cb 31.3bc 2.2

49.7 47.1c 30.3c 2.0

NA 32.2d 32.2a NA

85.2 57.3a 32.2a 2.9

78.1 54.2ba 31.2a 2.6

68.8 49.4b 30.1a 2.3

51.1 40.9c 30.1a 1.6

23.5 37.4c 32.2a 1.3

—not applicable; ND—not determined. Values are reported as means

d by same letter are not different (po0.05).

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Fig. 2 – Neutral detergent fiber (NDF) separation factors for elutriation of sieve categories of DDG and distillers dried grains

with solubles (DDGS).

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DDG. Original DDG had NDF of 36.7% (db), while enhanced

DDG would have NDF of 35.3% (db) and elusieve fiber would

have NDF of 57.3% (db).

Preliminary poultry nutrition studies on enhanced DDGS

from the elusieve process concluded that the process will

have positive effects by yielding a lower fiber, higher energy

and protein ingredient [10]. Similarly, enhanced DDG is also

expected to have higher inclusion levels in nonruminant

feeding because of lower NDF content in enhanced DDG than

in original DDG. Since DDG is the coproduct of dry-grind

plants where syrup is combusted for energy generation,

elusieve fiber separated from DDG is expected to be

used along with syrup for energy generation in these

plants. Elusieve fiber from DDGS was found to be a suitable

feedstock for producing ‘‘cellulosic’’ ethanol and corn fiber

gum [7,11]. Similarly, elusieve fiber separated from DDG

(coming from dry-grind plants that sell syrup as animal

feed instead of combusting) could perhaps have valuable use

as feedstock for production of ‘‘cellulosic’’ ethanol and corn

fiber gum.

4. Conclusions

The elusieve process was effective in separating fiber from

DDG. Elutriation increased NDF in the lighter fractions and

NDF separation factors were more than 1.0. When DDG is

separated via the elusieve process (based on 15% lighter

fraction yield from each of the four largest sieve categories),

11.9% would be obtained as elusieve fiber and 88.1% would

be obtained as enhanced DDG. Original DDG had NDF

of 36.7% (db), while enhanced DDG would have NDF of

35.3% (db) and elusieve fiber would have NDF of 57.3% (db).

Thus, the elusieve process produces value-added pro-

ducts from both DDG and DDGS. A detailed economic analysis

is needed to ascertain the merits of implementing

elusieve process in a dry-grind plant producing DDG instead

of DDGS.

Acknowledgment

This study was funded in part by the Illinois Council on Food

and Agricultural Research, Grant no. IDA CF 04E-072-1.

R E F E R E N C E S

[1] Lyons TP, Kelsall DR, Murtagh JE. The alcohol textbook:incorporating the alcohol alphabet. Nottingham, UK: Not-tingham University Press; 1995.

[2] Anon. Corn milling, processing and generation of coproducts.Minneapolis, MN: University of Minnesotta; October 2005/www.ddgs.umn.edu/davis-processing.pdfS.

[3] Nilles D. Natural gas. Ethanol Producer Magazine 2005;11:67–73.

[4] Anon. Official publication of AAFCO. Oxford, IN: The Associa-tion of American Feed Control Officials Incorporated; 2002.

[5] Morey RV, Tiffany DG, Hatfield DL. Biomass for electricity andprocess heat at ethanol plants. Applied Engineering inAgriculture 2006;22:723–8.

[6] Srinivasan R, Moreau RA, Rausch KD, Belyea RL, TumblesonME, Singh V. Separation of fiber from distillers dried grainswith solubles (DDGS) using sieving and elutriation. CerealChemistry 2005;82:528–33.

[7] Srinivasan R, Yadav MP, Belyea RL, Rausch KD, Pruiett LE,Johnston DB, et al. Fiber separation from distillers driedgrains with solubles using a larger elutriation apparatus anduse of fiber as a feedstock for corn fiber gum production.Journal of Biological Engineering, 2007, in press.

[8] Van Soest PJ, Robertson JB, Lewis BA. Methods for dietaryfiber, neutral detergent fiber, and nonstarch polysaccharidesin relation to animal nutrition. Journal of Dairy Science1991;74:3583–97.

ARTICLE IN PRESS

B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 4 6 8 – 4 7 2472

[9] Anon. Approved methods of the AACC. 10th ed. Minnesota:The American Association of Cereal Chemists;2000.

[10] Parsons CM, Martinez C, Singh V, Radhakrishnan S,Noll S. Nutritional value of conventional and modifiedDDGS for poultry. In: Multi-state poultry nutrition

and feeding conference, Indianapolis, IN, May 24–25,2006.

[11] Srinivasan R, Dien BS, Rausch KD, Tumbleson ME, Singh V.Fiber separated from distillers dried grains with solubles(DDGS) as a feedstock for ethanol production. CerealChemistry 2007;84:563–6.